The equipment necessary for refining operations is one of the major sources of costs in a refinery. The equipment can include catalytic reactors, fractionators and/or separators, and other supporting equipment. In a conventional process train, each catalytic reactor can have a dedicated fractionator or separator associated with the reactor, to separate out the various products produced in the catalytic reaction stage.
One method for saving on capital costs is to allow more than one reactor to use the same fractionator. U.S. Pat. No. 3,412,016 shows an example of a fractionator that includes multiple volumes. In this patent, two independent refinery gasoline streams (such as a low octane and a high octane gasoline) are fractionated in the fractionator. In the fractionator, the light ends portions of the two gasoline fractions are allowed to mix. However, there is no description or suggestion of any interaction, recycling, or other mixing of the gasoline “bottoms” portions. The outputs from the fractionator are a light fraction and the two distinct heavy fractions.
European Patent Publication No. EP 0819752 appears to provide another example of using a fractionator having multiple volumes. In this publication, it appears that two separate input streams are provided to the fractionator. The vapor portions produced in each side of the fractionator are allowed to mix, leading to production of one or more light product fractions from the fractionator. Each side of the fractionator also produces a bottoms portion. In some figures, the bottom portions appear to remain separated after leaving the fractionator, while in other figures the input to the second side of the fractionator includes portions of the bottoms from both sides of the fractionator.